1. Field of the Invention
The present invention relates to circuits for use with analog-to-digital converters (ADCs) and, in particular, to circuits that provide multirange output voltages for multiple ADCs.
2. Description of the Related Art
ADCs are used to convert an analog voltage to a digital signal. In some applications, the analog voltage has a magnitude which is proportional to the magnitude of an input signal to be monitored. For example, the input signal may be an input current flowing in a given current path. This input current may drive a primary winding of a current transformer, which produces a current in the secondary winding of the transformer, which is proportional to the input current. The secondary winding current may be applied to a known impedance, such as a resistance, to provide an analog voltage, which has a magnitude proportional to the magnitude of the secondary winding current and, thus, to the magnitude of the input current. The windings of the transformer and value of the resistance may be selected so that the range of the analog voltage for the expected range of the input current will be within the analog voltage input range of an ADC, which in turn converts the analog voltage to a digital signal, which can then be used to monitor the magnitude of the input current.
One problem with such conventional circuits utilizing ADCs is that the input signal to be monitored may have wide magnitude variations, which requires an ADC having a large dynamic range in order to accurately measure the signal's magnitude at both low and high levels. Unfortunately, ADCs capable of measuring a large dynamic range, for example larger than 10 bits, can be relatively expensive and thus unattractive.
Another problem exists in some configurations in which the secondary winding current is forced through a relatively large resistance, which causes a relatively large voltage signal to be produced when the secondary winding current is passed through the resistance. This imposes a large burden on the transformer, which could result in saturation, causing distortion and thus reducing the efficiency and performance of the transformer. Such large voltage signals can also cause damage to the ADC.